Light curing composite -a thermal risk for the pulp?

Abstract

Introduction and objectives: Light curing has shown to be a risk for the pulp as well as for superficial tissues due to high temperatures. The aim of this study was to evaluate temperature changes in a low viscosity bulk fill composite and the temperature effect on the pulp chamber temperature during light curing using a LED light curing device (LCU). The null hypothesis stated was that the composite tested would not have a thickness dependent temperature effect on pulp temperatures during light curing. Materials and methods: The composite used was SDRTM A mains powered LCU, Bluephase G2®, (was used for curing at high mode for 30 sec. The measurement and recordings of temperatures was performed using calibrated thermocouples. The study was divided in 3 parts (1-3) with curing cycles performed as follows: SDRTM was first cured (referred to as non-precured) and, after 5 minutes of recovery time, recured (referred to as precured). In part 1, a thermocouple was mounted in standard cylinders, filled with material and one curing cycle was performed. The curing cycles was repeated 5 times for each thickness. In part 2 the irradiance through SDRTM during curing cycles was evaluated using the same cylinders mounted on top of an irradiance tester. In part 3, evaluation of pulp chamber temperature in a caries-free 3:rd molar was done with a thermocouple inserted in the pulp chamber. A cavity was prepared close to the pulp chamber and controlled with X-ray. The root was immersed under water (36.4±1°C), composite placed and cured according to the protocol with 5 repeated measurements for each depth. The data were statistically analyzed with a One Way analysis of Variance with an alpha value of 0.05. Results: An increased difference in temperature between the non-precured and precured groups, with increased amount of SDRTM was shown. This was shown booth inside the SDRTM (part 1) and in the pulp chamber (part 3). Increased thickness of SDRTM placed in the cavity, lead to lower pulp chamber temperatures during light curing. Part 2 showed that the non-precured SDRTM absorbed more light than the precured SDRTM. Conclusion: SDRTM had a linear, thickness dependent effect on pulp chamber temperatures during light curing. A significant isolating effect was seen for increments above 3 mm of non-precured SDRTM, and for all groups of precured SDRTM. Potential tissue damaging pulp chamber temperatures were achieved when light curing was performed in an empty cavity and when thin increments of non-precured SDRTM were tested. The irradiance of the LCU, the absorption of irradiance in SDRTM, the exothermic reaction, and the conduction of heat from the material tested to the tooth, seemed to be the factors contributing to heat development in the pulp chamber during curing of the tested material.